St John's Ambulance recommends one 300mg tablet. Some others recommend 4x80mg tablets. they both work out to being a fairly low dose.
The instruction to chew those bitter pills is to get them into the blood stream faster.
The idea of them being already powdered is just fine, some doctors actually recommend crushing them.

Here is a quote from a medical college's web page on it.
"According to the American College of Emergency Physicians (ACEP), widespread use of aspirin for heart attack first aid could save 10,000 lives each year."